The present invention relates generally to memory cards, and more particularly, to a memory card (e.g., a secure digital card (SDC)) which includes a land grid array (LGA) structure and is fabricated through the implementation of a two-stage molding process such that the external signal contacts (ESC's) are located on a recessed plane within the memory card, and the exposed tie bars which are typical artifacts of traditional leadframe based memory cards are eliminated without compromising routability between the components.
As is well known in the electronics industry, memory cards are being used in increasing numbers to provide memory storage and other electronic functions for devices such as digital cameras, MP3 players, cellular phones, and Personal Digital Assistants. In this regard, memory cards are provided in various formats, including multi-media cards and secure digital cards.
Typically, memory cards include multiple electronic components such as integrated circuit devices, semiconductor dies, passive components, and the like. The components are often interconnected using a circuit board substrate which can accommodate complex routing. Memory cards also include electrical contacts or terminals for providing an external interface to an insertion point or socket. These electrical contacts are typically disposed on one side or face of the circuit board substrate, with the electrical connection to the components mounted to the substrate being provided by conductive vias and traces which extend through and along the substrate.
In certain memory cards, a leadframe assembly is used as an alternative to the circuit board substrate, as is described in Applicant's co-pending U.S. application Ser. No. 09/956,190 entitled LEAD-FRAME METHOD AND ASSEMBLY FOR INTERCONNECTING CIRCUITS WITHIN A CIRCUIT MODULE filed Sep. 19, 2001.
In those memory card configurations which in employ the use of the above-described substrate having one or more electrical devices or components mounted thereto, such components are typically covered or protected by a cap or lid (sometimes referred to as a “skin”) which is separately fabricated and attached to the substrate. The cap is typically fabricated through the implementation of an injection molding process, and is subsequently adhesively secured to the substrate in a manner covering or shielding the components mounted thereto. The cap is typically fabricated such that when mounted to the substrate, the resultant memory card meets or achieves a desired “form factor.” As will be recognized, the requirement of separately fabricating the cap and thereafter carrying out a separate process or step to mechanically couple the cap to the substrate increases the manufacturing cost for the prior art memory card, in addition to decreasing yield rate. This separate coupling process also increases the susceptibility of the internal components mounted to the substrate of being contaminated with various particles.
In addition to the foregoing, memory cards, such as secure digital cards, are used by advancing the same into a host socket which includes a plurality of connector pins. Many host sockets include a number of connector pins sufficient to accommodate the contacts included in various memory card formats. Though leadframe based memory cards possess certain advantages over circuit board based cards, one of the drawbacks associated with leadframe based memory cards is that portions of the tie bars which are used to connect the contacts and/or die pad(s) of the leadframe to the outer frame thereof are typically exposed in the leading edge and remaining side edges of the memory card. More particularly, exposed within the leading edge are the severed ends of the tie bars created as a result of the cutting or singulation process typically used to separate the outer frame of the leadframe from the remainder thereof subsequent to the formation of the body of the memory card. These exposed portions of the tie bars give rise to a potential to short against the metal features of the host socket, and are thus highly undesirable. Another limitation of the leadframe based memory card is routability. Leadframe based memory cards cannot accommodate complex component interconnections.
The present invention addresses and overcomes the aforementioned deficiencies of currently known memory cards by providing a memory card which includes a land grid array (LGA) structure and is fabricated through the implementation of a two-stage molding process such that the external signal contacts (ESC's) are located on a recessed plane within the memory card, and the exposed tie bars which are typical artifacts of traditional leadframe based memory cards are eliminated. The use of the two-stage molding process in the fabrication of the memory card of the present invention also effectively eliminates the need for the separate cap or lid of prior art memory cards, and provides a molded memory card with the desirable look of a lidded memory card. Further, the land grid array structure in the present memory card provides signal routing capability similar to that of a laminate substrate of a conventional memory card, but provides many of the cost/manufacturing economies of currently known leadframe based memory cards. Thus, the memory card of the present invention possesses the most desirable attributes of both laminate based, lidded memory cards and leadframe based, molded memory cards. These and other features of the present invention will be described in more detail below.